1. Field of the Invention
This invention relates to ink delivery systems. More particularly, this invention relates to a medium for ink delivery and filtration.
2. Description of Related Art
Existing ink delivery systems fail to provide and maintain a high quality print with good optical density, in large part, due to the break up and deterioration of existing foam and felt ink mediums used. The dislodged fibers, particles and debris are identified as a large cause of ink channel blocking. Ink channel blockage can result in ink drop out, missing jets, exploding jets and other jetting problems. Although wire mesh or filters have been used between the ink medium and the nozzle to filter particles, these filters suffer from inefficient filtration and blockage because particles, debris or fibers which are difficult to filter out bypass the filter. Also, the filters have a tendency to clog with particles, debris or fibers from the foam or felt that do not bypass the filter. The surface of the filter is difficult to clean once particles, debris or fibers have collected thereon. The clogging causes slow ink refill and air ingestion problems in the printhead resulting in slow print speed and poor ink jet print quality.
Melamine foam is a frequently used foam in ink delivery systems, as disclosed in U.S. patent application Ser. No. 07/885,704. However, although melamine foam has the advantage of low impedance and high efficiency, melamine foam can be dirty. Pieces of the foam may break off during use, and melamine foam may produce melamine dust. Therefore, use of melamine foam in ink delivery systems requires the use of filters. The melamine dust is difficult to filter out, is difficult to clean off a filter surface, and has a tendency to bypass and clog the ink channel, thereby causing the problems associated with ink blockage as discussed above. Accordingly, melamine foam must be precleaned prior to use. In addition, a finer filter, for example, a 9 micron filter is necessary in practical use to adequately filter the particles associated with melamine foam. Since melamine foam requires a finer filter, the impedance increases.
Reticulated foam is also unclean or dirty. During processing, the cells are broken by explosive reaction, and free material exists within the foam. Accordingly, reticulated foams must also be precleaned to filter out the free material. Precleaning, however, does not filter out all the free material and during use further breakage occurs generating more particles and debris. As a result, the problems discussed above relating to ink blockage occur.
Foams presently used in ink delivery systems, other than melamine foam, are formulated by a foaming process using surfactants. An expensive cleaning process is required to remove non-water soluble surfactants from the foams so that the foams can be used in ink delivery systems. Presently, a freon cleaning wash is used to clean foams. However, this cleaning process, and the residuals remaining after the cleaning process, must be disposed of properly to avoid negative environmental impacts.